Systems for providing fluid flow to tissues

ABSTRACT

Provided is an apparatus that includes a scaffold with a gel or liquid composition deposed on at least a portion of a luminal surface, the gel or liquid composition adapted to include microbubbles. Also provided is a system that includes a source of reduced pressure, the above scaffold, a manifold adjacent the scaffold, and a conduit for providing fluid communication between the manifold and the source of reduced pressure. Additionally provided is a method that includes implanting the above scaffold at the tissue site and disrupting a substantial portion of the microbubbles to induce fluid flow to the scaffold. Further provided is an apparatus that includes a scaffold that comprises a slowly degradable material and a quickly degradable material. Additionally provided is a system for coupling nerve tissue and a microchip assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/648,448, filed Dec. 29, 2009, entitled “Systems For Providing FluidFlow To Issues”, which claims the benefit of U.S. ProvisionalApplication No. 61/234,692, filed Aug. 18, 2009, U.S. ProvisionalApplication No. 61/142,053, filed Dec. 31, 2008, and U.S. ProvisionalApplication No. 61/142,065, filed Dec. 31, 2008, all of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present application relates generally to tissue engineering and inparticular to systems and scaffolds suitable for use in treatment oftissue.

2. Description of Related Art

Clinical studies and practice have shown that providing a reducedpressure in proximity to a tissue site augments and accelerates thegrowth of new tissue at the tissue site. The applications of thisphenomenon are numerous, but application of reduced pressure has beenparticularly successful in treating wounds. This treatment (frequentlyreferred to in the medical community as “negative pressure woundtherapy,” “reduced pressure therapy,” or “vacuum therapy”) provides anumber of benefits, including faster healing and increased formation ofgranulation tissue. Typically, reduced pressure has been applied totissue through a porous pad or other manifolding device. The porous padcontains pores that are capable of distributing reduced pressure to thetissue and channeling fluids that are drawn from the tissue. The porouspad often is incorporated into a dressing having other components thatfacilitate treatment. A scaffold can also be placed into a defect tosupport tissue growth into the defect. The scaffold is usuallybioabsorbable, leaving new tissue in its place.

Scaffolds for reduced pressure treatment are described in, e.g.,WO08/091521, WO07/092397, WO07/196590, WO07/106594. The adequacy ofcurrent scaffolds for reduced pressure treatment can be evaluated inlight of current knowledge of wound healing. Injury to body tissuesresults in a wound healing response with sequential stages of healingthat include hemostasis (seconds to hours), inflammation (hours todays), repair (days to weeks), and remodeling (weeks to months). A highlevel of homology exists across most tissue types with regards to theearly phases of the wound healing process. However, the stages ofhealing for various tissues begin to diverge as time passes, with theinvolvement of different types of growth factors, cytokines, and cells.The later stages of the wound healing response are dependent upon theprevious stages, with increasing complexity in the temporal patterningof and interrelationships between each component of the response.

Strategies to facilitate normal repair, regeneration, and restoration offunction for damaged tissues have focused on methods to support andaugment particular steps within this healing response, especially thelatter aspects of it. To this end, growth factors, cytokines,extracellular matrix (ECM) analogs, exogenous cells, and variousscaffolding technologies have been applied alone or in combination withone another. Although some level of success has been achieved using thisapproach, several key challenges remain. One main challenge is that thetiming and coordinated influence of each cytokine and growth factorwithin the wound healing response complicate the ability to addindividual exogenous factors at the proper time and in the correctcoordination pattern. The introduction of exogenous cells also facesadditional complications due to their potential immunogenicity as wellas difficulties in maintaining cell viability.

Synthetic and biologic scaffolds have been utilized to providethree-dimensional frameworks for augmenting endogenous cell attachment,migration, and colonization. To date nearly all scaffolds have beendesigned with the idea that they can be made to work with in situbiology. Traditional scaffolding technologies, however, rely on thepassive influx of endogenous proteins, cytokines, growth factors, andcells into the interstitium of the porous scaffold. As such, thecolonization of endogenous cells into the scaffold is limited by thedistance away from vascular elements, which provide nutrient supportwithin a diffusion limit of the scaffold, regardless of tissue type. Inaddition, the scaffolds can also elicit an immunogenic or foreign bodyresponse that leads to an elongated repair process and formation of afibrous capsule around the implant. Taken together, these complicationscan all lead to less than functional tissue regeneration at the injurysite.

It would therefore be advantageous to provide additional systems tofurther direct healing and tissue growth. The present invention providessuch systems.

BRIEF SUMMARY OF THE INVENTION

The scaffolds, systems and methods of the illustrative embodimentsdescribed herein provide active guidance of tissue regeneration throughan implanted scaffold. In one embodiment, an apparatus for providingreduced pressure therapy and facilitating growth of tissue at a tissuesite of a patient is provided that includes a scaffold adaptable forimplantation at the tissue site, where the scaffold provides astructural matrix for the growth of the tissue and having a luminalsurface, and a gel or liquid composition disposed on at least a portionof the luminal surface, the gel or liquid composition adapted to includemicrobubbles.

In another embodiment, a system for providing reduced pressure therapyand facilitating growth of tissue at a tissue site of a patient isprovided that includes a source of reduced pressure for supplyingreduced pressure, a scaffold adaptable for implantation at the tissuesite, where the scaffold provides a structural matrix for the growth ofthe tissue and has a luminal surface, a gel or liquid compositiondeposed on at least a portion of the luminal surface, where the gel orliquid composition is adapted to include microbubbles, a manifoldadjacent the scaffold, where the manifold distributes the reducedpressure to the scaffold, and a conduit for providing fluidcommunication between the manifold and the source of reduced pressure.

In a further embodiment, a method of providing reduced pressure therapyand facilitating growth of tissue at a tissue site of a patient isprovided that includes implanting a scaffold at the tissue site, wherethe scaffold provides a structural matrix for the growth of the tissueand comprises a gel or liquid composition on a luminal surface, wherethe gel or liquid composition is adapted to include microbubbles,applying reduced pressure to the scaffold, and disrupting a substantialportion of the microbubbles to induce fluid flow to the scaffold.

In an additional embodiment, an apparatus for providing reduced pressuretherapy and facilitating growth of tissue at a tissue site of a patientis provided that includes a scaffold adaptable for implantation at thetissue site, where the scaffold provides a structural matrix for thegrowth of the tissue and comprises a slowly degradable material, and aquickly degradable material, the quickly degradable material degradingfaster than the slowly degradable material to form channels in thescaffold for the transfer of a fluid, and a manifold for providingreduced pressure to the scaffold, where the channels provide fluidcommunication between the manifold and the tissue site.

In a further embodiment, a system for coupling nerve tissue and amicrochip assembly is provided that includes a source of reducedpressure, a biocompatible conduit adaptable for disposing adjacent nervetissue, where the conduit is fluidly coupled to the source of reducedpressure, and a microchip assembly disposed in the conduit, wherereduced pressure from the source of reduced pressure facilitates growthof the nerve tissue to operably connect to the microchip assembly.

Other objects, features, and advantages of the illustrative embodimentswill become apparent with reference to the drawings and detaileddescription that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system, shown in partial cross-section, for applying reducedpressure therapy to a tissue site of a patient;

FIG. 1A is a cross-section view of the system of FIG. 1 taken on theline 1A-1A;

FIGS. 2A-2C shows the scaffold in the system of FIG. 1 at differentpoints in time;

FIG. 3 is a cross-sectional view of a reduced pressure therapy apparatusin accordance with an illustrative embodiment;

FIG. 3A is a cross-sectional view of the apparatus of FIG. 3 taken onthe line 3A-3A; and

FIG. 4 is an illustrative embodiment of a system for connecting nervetissue with a microchip assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following detailed description of the illustrative embodiments,reference is made to the accompanying drawings that form a part hereof.These embodiments are described in sufficient detail to enable thoseskilled in the art to practice the invention, and it is understood thatother embodiments may be utilized and that logical structural,mechanical, electrical, and chemical changes may be made withoutdeparting from the spirit or scope of the invention. To avoid detail notnecessary to enable those skilled in the art to practice the embodimentsdescribed herein, the description may omit certain information known tothose skilled in the art. The following detailed description is,therefore, not to be taken in a limiting sense, and the scope of theillustrative embodiments are defined only by the appended claims.

Referring to FIGS. 1 and 2A-2C, a reduced pressure therapy system 100for applying reduced pressure to a tissue site 102 of a patient 103includes a reduced pressure source 106 that supplies reduced pressure, amanifold 108 fluidly coupled to the pressure source 106 via a conduit110, and a scaffold 112 in fluid communication with the manifold 108. Inthis example, the tissue site 102 is a bone 104 having a wound 105 thatis a gap in the diaphysis of the bone 104. The manifold 108 transfersthe reduced pressure to the scaffold 112 that is implanted within thewound 105 of the bone 104. The scaffold 112 may have a variety of shapesdepending on the type of wound, and in this embodiment has a tubularshape to fill the gap or wound 105 within the bone 104. The tubularscaffold 112 has a single lumen or flow channel 124 extending axiallythrough the scaffold 112 and having a luminal surface 114. The scaffold112 may also have a substantially cylindrical shape having a pluralityof lumens as necessary for growing new tissue within the wound 105.Ultimately, the scaffold 112 is colonized by cells and matrix proteinsthat flow primarily from the intramedullary space 122 of the bone 104through the flow channel 124 in response to application of the negativepressure or other stimuli.

The luminal surface 114 of the scaffold 112 is coated with a chemicalsubstance 116 having a solid, gelatinous, or liquid form that containsmicrobubbles 118 (not shown). The chemical substance 116 may include themicrobubbles 118 that are pre-formed in the chemical substance 116 whenapplied to the luminal surface 114 of the flow channel 124. In otherembodiments, the chemical substance 116 may comprise a composition thatforms the microbubbles 118 after being applied to the luminal surface114 of the flow channel 124 as a result of portions of the chemicalsubstance 116 transitioning into a gaseous phase, i.e., a gaseous phasetransition, in response to a stimulus or catalyst. After the scaffold112 is implanted within the wound 105, the microbubbles 118 aredisrupted as part of the therapy to induce fluid flow from theintramedullary space 122, through the flow channel 124 and into thescaffold 112 as identified by arrows 126.

FIGS. 2A to 2C show the scaffold 112 and the chemical substance 116 atthree different points in time. FIG. 2A shows the scaffold 112 and thechemical substance 116 disposed on the luminal surface 114 before themicrobubbles 118 are formed and before the induction of a gaseous phasetransition. FIG. 2B shows the chemical substance 116 containing themicrobubbles 118 that were already formed when initially applied to theluminal surface 114, or were formed after application upon induction ofa gaseous phase transition. The microbubbles 118 may be formed by avariety of stimuli such as, for example, by utilizing a chemicalsubstance 116 that is responsive to high-frequency ultrasound and thenexposing the chemical substance 116 to such ultrasound frequencies tocreate the microbubbles either before or after the chemical substance116 is disposed on the luminal surface 114. Microbubbles 118 may also beformed by other stimuli including, for example, heat provided by anexternal source or the body itself, light energy, mechanicalstimulation, or chemical stimulation.

When the microbubbles 118 are pre-formed in the chemical substance 116,implantation and the consequential heating of the scaffold 112 to bodytemperature may increase the size of pre-formed microbubbles 118 asdescribed in WO 2006/12753. When the microbubbles 118 are notpre-formed, the gaseous phase transition of the chemical substance 116may be induced by a temperature increase resulting from implanting thescaffold 112 into the wound 105 which is at a higher body temperature.In some embodiments, the chemical substance 116 has a composition thatinduces the gaseous phase transition at the body temperature of themammal (e.g., 37° C. for humans). In other embodiments, the gaseousphase transition may be induced by sound waves or ultrasonic waveshaving a relatively low frequency within the range of about 20 kHz toabout 500 kHz for example. The optimum wavelength for any particularchemical substance 116 can be determined by routine experimentation.Whatever method of induction is used, the gaseous phase transition canbe induced either before or after implantation of the scaffold. Themicrobubbles 118 may be formed by a gaseous component of the chemicalsubstance 116 such as, for example, perfluoropentane (C₅F₁₂) ordecafluorobutane (C₄F₁₀). The microbubbles 118 are bubbles that are lessthan about 100 μm in diameter. In some embodiments, the microbubbles 118are between about 1 μm in diameter and about 75 μm in diameter.

Any biocompatible gas may be used in the formation of the microbubbles118, including nitrogen, oxygen, carbon dioxide, hydrogen, an inert gas(e.g., helium, argon, xenon or krypton), a sulfur fluoride (e.g., sulfurhexafluoride), an optionally halogenated silane such as methylsilane ordimethylsilane, a low molecular weight hydrocarbon such as an alkane, acycloalkane, an alkene, an ether, a ketone, an ester, a halogenated lowmolecular weight hydrocarbon, or a mixture of any of the foregoing. Insome embodiments, the gas used to form the microbubbles 118 comprisesfluorine atoms, e.g., bromochlorodifluoromethane, chlorodifluoromethane,dichlorodifluoromethane, bromotrifluoromethane, chlorotrifluoromethane,chloropentafluoroethane, dichlorotetrafluoroethane,chlorotrifluoroethylene, fluoroethylene, ethylfluoride, sulfurhexafluoride, 1,1-difluoroethane and perfluorocarbons, e.g.,perfluoropropane, perfluorobutanes and perfluoropentanes.

The microbubbles 118 may be formed by mixing a gas, or a compound thatis a gas at body temperature, with an amphiphilic compound or asurfactant. See, e.g., PCT Patent Publication WO 2006/127853 and U.S.Patent Application Publication US 2005/0260189, both incorporated byreference. The surfactant in the chemical substance 116 used to form themicrobubbles 118 may comprise a single compound or a combination ofcompounds. Examples of useful surfactants include lipids, includingsterols, hydrocarbons, fatty acids and derivatives, amines, esters,sphingolipids, and thiol-lipids; block copolymers of polyoxypropylene;polyoxyethylene; sugar esters; fatty alcohols, aliphatic amine oxides;hyaluronic acid aliphatic esters and salts thereof, dodecylpoly-(ethyleneoxy)ethanol; nonylphenoxy poly(ethyleneoxy)ethanol;hydroxy ethyl starch; hydroxy ethyl starch fatty acid esters; dextrans;dextran fatty acid esters; sorbitol; sorbitol fatty acid esters;gelatin; serum albumins; phospholipid-containing surfactants (e.g.,lecithins [phosphatidylcholines, dimyristoylphosphatidylcholine,dipalmitoylphosphatidylcholine or distearoylphosphatidylcholine, etc.],phosphatidic acids, phosphatidylethanolamines, phosphatidylserines,phosphatidylglycerols, phosphatidylinositols, cardiolipins,sphingomyelins); nonionic surfactants such aspolyoxyethylene-polyoxypropylene copolymers, e.g., Pluronic surfactants;polyoxyethylene fatty acids including polyoxyethylene stearates,polyoxyethylene fatty alcohol ethers, polyoxyethylated sorbitan fattyacid esters, glycerol polyethylene glycol oxystearate, glycerolpolyethylene glycol ricinoleate, ethoxylated soybean sterols,ethoxylated castor oils, and the hydrogenated derivatives thereof;cholesterol; anionic surfactants. In some embodiments, the amphiphilicsubstance is a block copolymer, for example (poly(ethyleneoxide)-block-poly(L-lactide)) (PEG-PLLA), poly(ethyleneoxide)-block-poly(caprolactone)), or Pluronic P-105. In addition to thesurfactant(s), other agents may be incorporated within the aqueous phaseof the chemical substance 116. Such agents include conventionalviscosity modifiers, buffers such as phosphate buffers or otherconventional biocompatible buffers or pH adjusting agents such as acidsor bases, osmotic agents (to provide isotonicity, hyperosmolarity, orhyposmolarity).

In some embodiments, the chemical substance 116 may further comprise abioactive agent which may be contained within the microbubbles 118,where the bioactive agent is released when the microbubbles 118 aredisrupted. The microbubbles 118 may encapsulate the bioactive agentwhich can be released depending on the therapy wherein the microbubbles118 are disrupted as described below in more detail. The bioactive agentmay also be present within the chemical substance 116 outside of themicrobubbles 118, such as in solution or encapsulated in micelles of thesurfactant, where the agent is slowly released (See, e.g., WO2006/127853). In some embodiments, the bioactive agent is an antibioticor a growth factor. Nonlimiting examples of useful bioactive growthfactors for various applications are growth hormone (GH), a bonemorphogenetic protein (BMP), transforming growth factor-α (TGF-α), aTGF-β, a fibroblast growth factor (FGF), granulocyte-colony stimulatingfactor (G-CSF), granulocyte/macrophage-colony stimulating factor(GM-CSF), epidermal growth factor (EGF), platelet derived growth factor(PDGF), insulin-like growth factor (IGF), vascular endothelial growthfactor (VEGF), hepatocyte growth factor/scatter factor (HGF/SF), aninterleukin, tumor necrosis factor-α (TNF-α) or nerve growth factor(NGF).

FIG. 2C shows the scaffold 112 and the chemical substance 116 afterbeing subjected to a stimulus that disrupts the microbubbles 118 so thatthey rupture or collapse to facilitate fluid flow as represented by thearrows 126 through the flow channel 124 and the chemical substance 116into the scaffold 112 as described above. The microbubbles 118 may bedisrupted by a variety of stimuli such as, for example, by exposing themicrobubbles 118 to high frequency ultrasound having a frequency in therange of about 1 MHz to about 5 MHz. Disruption of the microbubbles 118creates openings in the chemical substance 116 that provide an increasedarea for fluids to occupy and that may also form passages forfacilitating or enhancing fluid flow as described above including bothgaseous fluid flow and liquid fluid flow such as fluid flow from thewound 105. In some embodiments, the direction of fluid flow can becontrolled by concentrating the microbubbles 118 in different portionsof the chemical substance 116 to direct flow toward a predeterminedportion of the scaffold 112. In other embodiments, directional flow isenhanced by disrupting the microbubbles 118 sequentially acrosscontiguous segments of the scaffold 112 to create directional changes inthe fluid flow 126.

The term “scaffold” as used herein refers to a substance that provides astructural matrix for the growth of cells and/or the formation oftissue. A scaffold is often a three dimensional porous structure thatmay be infused with, coated with, or comprised of cells, growth factors,extracellular matrix components, nutrients, integrins, or othersubstances to promote cell growth. A scaffold can take oncharacteristics of a manifold by directing flow through the matrix. Thescaffold 112 may have a variety of shapes including, for example, asubstantially cylindrical shape such as a conduit fabricated forgenerating nerve fibers. An example of such a scaffold is described inU.S. Provisional Patent Applications 61/142,053 and 61/142,065. Thescaffold 112 can be used in any tissue engineering application thatcould benefit from directed flow. Such scaffolds are useful for example,for encouraging long bone growth or for nerve regeneration, as discussedin U.S. Provisional Patent Application 61/142,053.

Nonlimiting examples of suitable scaffold 112 materials includeextracellular matrix proteins such as fibrin, collagen, or fibronectin,and synthetic or naturally occurring polymers, including bioabsorbableor non-bioabsorbable polymers, such as polylactic acid (PLA),polyglycolic acid (PGA), polylactide-co-glycolide (PLGA),polyvinylpyrrolidone, polycaprolactone, polycarbonates, polyfumarates,caprolactones, polyamides, polysaccharides (including alginates [e.g.,calcium alginate] and chitosan), hyaluronic acid, polyhydroxybutyrate,polyhydroxyvalerate, polydioxanone, polyorthoesthers, polyethyleneglycols, poloxamers, polyphosphazenes, polyanhydrides, polyamino acids,polyortho esters, polyacetals, polycyanoacrylates, polyurethanes,polyacrylates, ethylene-vinyl acetate polymers and other acylsubstituted cellulose acetates and derivatives thereof, polystyrenes,polyvinyl chloride, polyvinyl fluoride, polyvinylimidazole,chlorosulphonated polyolefins, polyethylene oxide, polyvinyl alcohol,Teflon®, hydrogels, gelatins, and nylon. The scaffold 112 can alsocomprise ceramics such as hydroxyapatite, coralline apatite, calciumphosphate, calcium sulfate, calcium carbonate or other carbonates,bioglass, allografts, autografts, xenografts, decellularized tissues, orcomposites of any of the above. In particular embodiments, the scaffold112 comprises collagen, polylactic acid (PLA), polyglycolic acid (PGA),polylactide-co-glycolide (PLGA), a polyurethane, a polysaccharide, anhydroxyapatite, or a polytherylene glycol. Additionally, the scaffold112 can comprise combinations of any two, three, or more materials,either in separate areas of the scaffold 112, or combined noncovalently,or covalently combined (e.g., copolymers such as a polyethyleneoxide-polypropylene glycol block copolymers, or terpolymers), orcombinations thereof. Suitable matrix materials are discussed in, forexample, Ma and Elisseeff, 2005, and Saltzman, 2004.

Referring now to FIG. 3, another embodiment of a reduced pressuretherapy system 300 having components similar to the reduced pressuretherapy system 100 as shown by common numeric references. The reducedpressure system 300 comprises a scaffold 312 in fluid communication withthe manifold 108 having all the characteristics of the scaffold 112described above including, without limitation, a single lumen or flowchannel 324 having a luminal surface 314. The luminal surface 314 mayalso be coated with a chemical substance 116 (not shown) containingmicrobubbles 118 as described above. The scaffold 312 may be formed frombioabsorbable materials that degrade at different rates to furtherenhance fluid flow through the scaffold 312. For example, the scaffoldmay be formed primarily from a first material or structural material 328that may be degradable and a second material that degrades more quicklythan the first material, i.e., degradable material such as, for example,a hydrocolloid that degrades in less than a day or two. The secondmaterial that degrades more quickly than the structural material 328 maybe fabricated in the form of a channel 330 extending generally radiallyfrom the luminal surface 314 to the manifold 108. When the channel 330of material degrades after the scaffold 312 is implanted within thewound 105, channel passages 332 are formed through the scaffold 312 tofurther facilitate the flow of fluids from the intramedullary space 122,through the flow channel 324, and into and through the scaffold 312.

The second material may also be formed in pockets 334 dispersedthroughout the structural material 328 of the scaffold 312. The pockets334 of degradable material may be used in addition to, or in lieu of,the channels 330 of degradable material and may degrade at a differentrate when used in conjunction with the channels 330. When the pockets334 of degradable material degrade after the scaffold 312 is implantedwithin the wound 105, pores (not shown) are formed in the structuralmaterial 328 that can absorb more fluids and/or provide passages tofurther facilitate fluid flow in addition to the channel passages 332from the intramedullary space 122 to the manifold 108.

As indicated above, when the scaffold 312 is implanted in the wound anda reduced pressure is applied through the manifold 108, reduced pressuregradients flow through the scaffold 312 from the intramedullary space122 of the bone 104 through the flow channel 324 and the channelpassages 332 to facilitate the flow of fluids for delivering cells andbeneficial proteins (e.g., growth factors and structural proteins)contained within the fluid into the scaffold 312. As the pockets 334 ofdegradable material dissolve, the pores in the structural material 328of the scaffold 312 absorb the fluid from the intramedullary space 122accelerating cell colonization of the scaffold 312. It should beunderstood that the pores in the structural material 328 and the channelpassages 332 may be a permeable matrix of material after degradationhaving a permeability selected to control the rate at which the scaffold312 absorbs such fluids. In other embodiments, the pores in thestructural material 328 may be substantially void, and the channelpassages 332 may also be substantially void or narrow, to furtherenhance the flow of fluid through the scaffold 312 and into the manifold108.

Wound healing and tissue engineering can benefit from changing flowpatterns as healing or tissue production/remodeling proceeds. Further,clogging of pores in the scaffold 312 and the channel passages 332 cancause flow through the scaffold 312 to decrease over time if no flowadjustments are made. Thus, therapy for treating the wound 105 canchange over time. For example, based on the sequential stages ofhealing, i.e., hemostasis (seconds to hours), inflammation (hours todays), repair (days to weeks), and remodeling (weeks to months), a freshwound (e.g., post surgery) would benefit from the provision of an agentthat encourages hemostasis (e.g., platelet-activating factor, PAF) onlyif that agent were provided when healing first commenced, and would notbe beneficial if only provided days after the wound was made.Conversely, an agent involved in repair or remodeling, e.g., TGF-β,would be optimally beneficial if provided after a day or two.

The structural material 328 of the scaffold 312 may be selected from avariety of degradable materials as long as they degrade more slowly thanthe channels 330 of degradable material. In one embodiment, thestructural material 328 does not degrade completely for sixty days,while the channels 330 and/or pockets 334 of degradable material maydegrade fully over a time period less than sixty days down to a day. Thestructural material 328 may be a biocompatible material that essentiallydoes not degrade, such as metals or polyetheretherketone (PEEK). In someembodiments, the scaffold 312 is formed of structural material 328 thatis already porous in addition to the channels 330 and/or pockets 334 ofdegradable material so that the porous structural material 328accelerates fluid flow into and through the scaffold 312 and providesalternate passages for the fluid if the pores and channel passages 332become clogged or blocked. The porous structural material 328 has poresaveraging in size between about 50 and 500 microns. In otherembodiments, the structural material 328 is not porous, and thedegradation of the degradable material in the channels 330 and pockets334 serve to commence flow through the scaffold 312. The scaffold 312may be manufactured by a variety of processes as suitable for theselected material including, for example, those processes referred toabove and further including salt leaching, freeze-drying, phaseseparation, weaving fibers, bonding non-woven fibers, or foaming.

In some embodiments, the degradable material of the channels 330 andpockets 334 comprise a hydrocolloid, such as those comprising anaturally occurring or chemically modified polysaccharide. Suitablechemically modified polysaccharides include carboxymethylcellulose gels,hydroxyethyl cellulose gels, hydroxy-propyl methyl cellulose gels,chitosan, low-methoxy pectins, cross-linked dextran andstarch-acrylonitrile graft copolymer, starch sodium polyacrylate, andmixtures thereof. Suitable natural polysaccharides include alginic acidand its salts, pectins, galactomannans such as xanthan gum or guar gumlocust bean gum, gum karaya, gum arable, hyaluronic acid and its salts,starches, and mixtures thereof. Suitable synthetic hydrocolloids includehigh molecular weight polyethylene glycols and polypropylene glycols,polymers of methyl vinyl ether and maleic acid and derivatives;polyvinyl pyrrolidone, polyethylene glycols, polypropylene glycols,metal and/or ammonium salts of polyacrylic acid and/or its copolymers,metal or ammonium salts of polystyrene sulfonic acid, and mixturesthereof.

The degradable material of the channels 330 and the pockets 334, as wellas the structural material 328 to the extent degradable, may furthercomprise a bioactive agent, such as an antibiotic or a growth factor,including those discussed above. In some embodiments of the scaffold312, the channels 330, and the pockets 334, as well as the structuralmaterial 328 to the extent degradable, may include more than one type ofdegradable material such as, for example, materials that degrade at twodifferent rates to control the patterns of fluid flow for depositingcells or releasing bioactive agents in a predetermined pattern for thetherapy being administered to the patient 103. For example, the channels330 closest to the diaphysis of the bone 104 may be formed of materialthat degrades faster than the channels 330 in the center of the scaffold312 to accelerate fluid flow at those locations, thereby acceleratingthe healing of the wound 105.

As indicated above, wound healing and tissue engineering can benefitfrom changing flow patterns as healing or tissue production/remodelingproceeds. Clogging of the pores in the scaffold 312 and the channelpassages 332 can cause fluid flow through the scaffolding 312 todecrease over time if no flow adjustments are made. Consequently, thescaffold 312 may also include reduced pressure chambers 340 that whenpunctured or ruptured stimulate the flow of fluids and proteins alongdesired pathways 341 toward a central reduced pressure source such asthe manifold 108. These low pressure chambers 340 can be of any shapesuch as, for example, spherical or elliptical, and contain a pressurethat is lower than the ambient pressure within the scaffold 312. Thepressure is sufficiently low within the low pressure chamber 340 so thatthe chambers 340 further induce fluid flow from the intramedullary space122, through the flow channel 324, and into and through the scaffold 312when the chambers 340 rupture and open. The low pressure chambers 340are also useful for unclogging pores in the scaffold 312 and the channelpassages 332 to facilitate fluid flow through the scaffold 312 as a flowadjustment during the therapy period for treating the wound 105.

The wound 105 may be an injury or defect, such as a fracture, located onor within any tissue site 102, including but not limited to, bonetissue, adipose tissue, muscle tissue, neural tissue, dermal tissue,vascular tissue, connective tissue, cartilage, tendons or ligaments. Forexample, the wound 105 can include burns, incisional wounds, excisionalwounds, ulcers, traumatic wounds, and chronic open wounds. The wound 105may also be any tissue that is not necessarily injured or defected, butinstead is an area in which it is desired to add or promote growth ofadditional tissue, such as bone tissue. For example, reduced pressuretissue treatment may be used in certain tissue areas to grow additionaltissue that may be harvested and transplanted to another tissuelocation. The tissue site 102 may also include sites for in vitro and invivo maintenance of endogenous or exogenous grafts, and supportivescaffolds for subsequent implantation into the patient 103. The patient103 may be any mammal, such as a mouse, rat, rabbit, cat, dog, orprimate, including humans.

In the context of this specification, the term “reduced pressure”generally refers to a pressure that is less than the ambient pressure ata tissue site that is subjected to treatment. In most cases, thisreduced pressure will be less than the atmospheric pressure where thepatient is located. Although the terms “vacuum” and “negative pressure”may be used to describe the pressure applied to the tissue site, theactual pressure applied to the tissue site may be significantly greaterthan the pressure normally associated with a complete vacuum. Consistentwith this nomenclature, an increase in reduced pressure or vacuumpressure refers to a relative reduction of absolute pressure, while adecrease in reduced pressure or vacuum pressure refers to a relativeincrease of absolute pressure. Reduced pressure treatment typicallyapplies reduced pressure at −5 mm Hg to −500 mm Hg, more usually −5 to−300 mm Hg, including but not limited to −50, −125, or −175 mm Hg.

The term “manifold” as used herein generally refers to a substance orstructure that is provided to assist in applying reduced pressure to,delivering fluids to, or removing fluids from the tissue site 102. Themanifold 108 typically includes a plurality of flow channels or pathwaysthat distribute fluids provided to and removed from the tissue site 102around the manifold 108. In one illustrative embodiment, the flowchannels or pathways are interconnected to improve distribution offluids provided or removed from the tissue site 102. The manifold 108may be a biocompatible material that is capable of being placed incontact with the tissue site 102 and distributing reduced pressure tothe tissue site 102. Examples of manifolds 108 may include, for example,without limitation, devices that have structural elements arranged toform flow channels, such as, for example, cellular foams, open-cellfoams, porous tissue collections, liquids, gels, and foams that include,or cure to include, flow channels. The manifold 108 may be porous andmay be made from foam, gauze, felted mat, or any other material suitedto a particular biological application. In one embodiment, the manifold108 is a porous foam and includes a plurality of interconnected cells orpores that act as flow channels. The porous foam may be a polyurethane,open-cell, reticulated foam such as GranuFoam®, manufactured by KineticConcepts, Inc. of San Antonio, Tex. Other embodiments might include“closed cells.” These closed-cell portions of the manifold may contain aplurality of cells, the majority of which are not fluidly connected toadjacent cells. The closed cells may be selectively disposed in themanifold 108 to prevent transmission of fluids through perimetersurfaces of the manifold 108. In some situations, the manifold 108 mayalso be used to distribute fluids such as medications, antibacterials,growth factors, and various solutions to the wound 105. Other layers maybe included in or on the manifold 108, such as absorptive materials,wicking materials, hydrogels, hydrophobic materials, and hydrophilicmaterials.

As described above, the reduced pressure therapy system 100 appliesreduced pressure to the wound 105 which may be distributed uniformlythrough the scaffold 112. In some embodiments, the scaffold distributesreduced pressure discontinuously through the scaffolds 112 and 312rather than being distributed in some uniform fashion thereby creating areduced pressure gradient. For example, the reduced pressure is notdelivered uniformly via a single point source, or via a plurality ofinlets along a linear flow passage, or through a substantiallyhomogeneous distribution manifold. In some embodiments, the reducedpressure gradient is discontinuous spatially, discontinuous inmagnitude, or discontinuous over time. Consequently, the reducedpressure gradients may occur throughout the wound 105.

A gradient is the rate of change of any variable physical quantity inaddition to reduced pressure including, without limitation, biologicgradients, thermal gradients, electrical gradients, magnetic gradients,chemical gradients, or positive pressure gradients. The manifold 108 andthe scaffolds 112 and 312 may be designed to distribute gradients forthese other physical characteristics. Referring to FIGS. 1A and 3A, forexample, the manifold 108 and the scaffolds 112 and 312 may distributereduced pressure gradients and/or biologic gradients as indicated by thearrows 126 and 326, respectively, as described above in more detail andas further described in U.S. Provisional Patent Applications 61/142,053and 61/142,065, which are hereby incorporated by reference. Thecircumferential scaffolds 112 and 312 draw fluid radially from theintramedullary space 122 of the bone 104 (not shown) through theirrespective flow channels 124 and 324 in response to the reduced pressureor other stimuli, but in a discontinuous fashion to create gradients tofurther promote tissue growth and/or tissue healing. Thus, the methodsand systems of the present invention provide a means for active guidanceof tissue regeneration through the implanted scaffolds 112 and 312 orwithin a compromised site, such as wound 105, to promote functionalrecovery utilizing these physical gradients. As such, these methods andsystems provide an active mechanism by which to promote the endogenousdeposition of proteins and organization of the provisional matrix withbiochemical and physical cues to direct cellular colonization of thescaffolds 112 and 312 or tissue space within the wound 105.

Referring to FIG. 4, an illustrative embodiment of a system 436 forcoupling nerve tissue 438 to a microchip assembly 440 is shown. Thenerve tissue 438 of this embodiment may have been damaged as a result oftrauma so that only one severed end 439 remains. As used herein, theterm “coupled” includes indirect coupling via a separate object andincludes direct coupling. The term “coupled” also encompasses two ormore components that are continuous with one another by virtue of eachof the components being formed from the same piece of material. Also,the term “coupled” may include chemical, mechanical, thermal, orelectrical coupling. Fluid coupling means that fluid is in communicationbetween the designated parts or locations.

The microchip assembly 440 and the severed end 439 of the nerve tissue438 are positioned within a biocompatible nerve conduit 442 that isgenerally tubular in shape for receiving and sealing the nerve tissue438 at one end and closed by a conduit end wall 443 at the other end toform a luminal space 445 between the severed end 439 of the nerve tissue438 and the conduit end wall 443. The microchip assembly 440 has acontact surface 441 positioned adjacent the severed end 439 and iselectrically coupled to an electronic control unit 448 via a connection449 that runs through the conduit end wall 443. The connection 449 thatelectrically couples the electronic control unit 448 to the microchipassembly 440 may be, for example, a hard-wire connection or a wirelessconnection. The electronic control unit 448 may also include a battery450 for providing power to the microchip assembly 440 via the connection449. It should be understood that both the electronic control unit 448and the battery 450 may be integrated with the microchip assembly 440within the luminal space 445 inside the nerve conduit 442.

The nerve conduit 442 is fluidly coupled to a reduced pressure source456 via a conduit 459 and a manifold 458 that distributes reducedpressure from the reduced pressure source 456 to the luminal space 445.The reduced pressure in the luminal space 445 provides a flow pattern tothe severed end 439 of the nerve tissue 438 and its interface with thecontact surface 441 of the microchip assembly 440 to promote growthand/or regeneration of the nerve tissue 438. More specifically, thereduced pressure causes the fibers in the nerve tissue 438 to grow andoperatively connect to the contact surface 441 of the microchip assembly440. The manifold 458 may be bioresorbable to facilitate removal of theconduit 459 after the nerve tissue 438 has operatively connected to thecontact surface 441 of the microchip assembly 440. The nerve conduit 442itself may also be bioresorbable after sufficient healing of the nervetissue 438 so that it does not need to be removed to avoid disruptingthe operative connection between the severed end 439 of the nerve tissue438 and the contact surface 441 of the microchip assembly 440.

The electronic control unit 448 controls a prosthetic or orthotic device(not shown) such as an artificial hand. To control the prosthetic ororthotic device, the electronic control unit 448 may include a radiofrequency (RF) transceiver for sending radio signals to the prostheticor orthotic device. In other embodiments, the electronic control unit448 may be contained within the prosthetic or orthotic device fordirectly controlling movement. The connection between the severed end439 of nerve tissue 438 and the contact surface 441 of the microchipassembly 440 allows a patient to control movement of such devices usingthought-controlled nerve firing as an input for the regenerated nervetissue 438 via the microchip assembly 440. The system 436 may be used asan interface device to restore motor control after nerve trauma, or toestablish nerve-directed motor control of an orthotic or prostheticdevice.

REFERENCES

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All references cited in this specification are hereby incorporated byreference. The discussion of the references herein is intended merely tosummarize the assertions made by the authors and no admission is madethat any reference constitutes prior art. Applicants reserve the rightto challenge the accuracy and pertinence of the cited references.

In view of the above, it will be seen that the advantages of theinvention are achieved and other advantages attained. As various changescould be made in the above methods and compositions without departingfrom the scope of the invention, it is intended that all mattercontained in the above description and shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

We claim:
 1. A method for providing reduced pressure to a tissue site tofacilitate tissue growth, the tissue site comprising a gap in thediaphysis of a bone, the method comprising: providing a scaffold, thescaffold being tubular in shape and having a luminal surface forming atleast one channel, the at least one channel at least partially coveredby a chemical substance containing microbubbles; implanting the scaffoldin the tissue site so that the at least one channel is in direct fluidcommunication with an intramedullary space of the tissue site; providingreduced pressure to the tissue site through the scaffold; and disruptinga substantial portion of the microbubbles to induce the flow of fluidswithin the scaffold.
 2. The method of claim 1, wherein the chemicalsubstance forms microbubbles in response to a stimulus that induces agaseous phase transition in the chemical substance.
 3. The method ofclaim 1, wherein the microbubbles are pre-formed in the chemicalsubstance.
 4. The method of claim 1, further comprising: inducing agaseous phase transition in the chemical substance to form themicrobubbles after implanting the scaffold.
 5. The method of claim 4,wherein inducing the gaseous phase transition in the chemical substanceincludes exposing the chemical substance to the body temperature of thepatient.
 6. The method of claim 1, wherein disrupting the substantialportion of the microbubbles includes inducing gradients in the reducedpressure.
 7. The method of claim 1, wherein disrupting the substantialportion of the microbubbles includes inducing directional changes in thereduced pressure by sequentially disrupting the microbubbles acrosscontiguous segments of the scaffold.
 8. The method of claim 1, whereindisrupting the substantial portion of the microbubbles includes exposingthe chemical substance to ultrasound energy.
 9. The method of claim 1,wherein disrupting the substantial portion of the microbubbles includesexposing the chemical substance to light energy.
 10. The method of claim1, wherein the scaffold includes pre-formed low-pressure chambers andthe method further comprises rupturing the pre-formed low-pressurechambers.